Use of glycerol-cryoprotected Lactobacillus casei for microbiological assay of folic acid.
A simple procedure for preparing glycerol-cryoprotected Lactobacillus casei cultures has been developed. L. casei grown in medium supplemented with low concentrations of folic acid (0.3 micrograms/L) is diluted with an equal volume of glycerol (800 mL/L) and stored at -20 degrees C.  Growth response of the glycerol-cryoprotected L. casei to low concentrations of folic acid exceeded that of cultures maintained by monthly agar stab transfer. Also, growth for the zero-folate blanks was considerably less for the cryoprotected cultures. Assay of folate in several rat tissues correlated well (r = 0.999) with the standard microbiological assay. The growth rate of the culture depends on the inoculum size, and a heavy inoculum of cryoprotected L. casei may be used to complete the assay after only an overnight incubation.
D000818:Animals; D001923:Brain Chemistry; D005492:Folic Acid / Q000032:analysis*; D007668:Kidney / Q000032:analysis; D007780:Lacticaseibacillus casei; D008099:Liver / Q000032:analysis; D008297:Male; D008828:Microbiological Techniques; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values; D013997:Time Factors
D005492:Folic Acid